1. Field of the Invention
The invention relates to an internal combustion engine control apparatus and an internal combustion engine control method. In particular, the invention relates to an apparatus and a method for controlling an internal combustion engine in which a valve timing control for early closing of exhaust valves is executed.
2. Description of the Related Art
Japanese Patent Application Publication No. 2004-92639 (JP-A-2004-92639) describes a valve tinting control apparatus for an internal combustion engine incorporating a variable valve timing mechanism capable of variably controlling the timing for opening and closing exhaust valves. This valve timing control apparatus controls, under a given operation condition, the exhaust valves to be closed before the intake stroke top dead center (this control will be referred to as “exhaust-valve-early-closing valve timing control” where necessary). According to this exhaust-valve-early-closing valve timing control, the gas remaining in each combustion chamber after failing to be discharged to the exhaust gas passage on the exhaust stroke (will be referred to as “residual gas” where necessary) can be subjected to combustion again. As such, unburned hydrocarbon contained in the residual gas is combusted again, and this reduces the exhaust emissions.
Meanwhile, when an internal combustion engine is idling after running at high load, the temperature in the engine compartment of the vehicle tends to be relatively high, and thus the temperature of the engine coolant tends to be relatively high. Further, during the foregoing exhaust-valve-early-closing valve timing control, the aforementioned high-temperature residual gas, which has been subjected to combustion on the power stroke and then recompression on the exhaust stroke, is brought back into the intake passage and then drawn again into the combustion chamber. Therefore, in an internal combustion engine in which the foregoing exhaust-valve-early-closing control is executed, if the internal combustion engine is placed in the idling state after running at high load, the temperature of combustion gas tends to be relatively high. If the internal combustion engine is reaccelerated in this state, engine knocking (will be referred to as “start engine knocking” where necessary) may occur.